Re: Wrong

From:

Joshua Maurice <joshuamaurice@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 17 Apr 2010 23:13:53 -0700 (PDT)

Message-ID:

<4e005e43-93de-4969-9b0b-98b4046c0693@8g2000yqz.googlegroups.com>

On Apr 17, 8:36 pm, "Alf P. Steinbach" <al...@start.no> wrote:

* Joshua Maurice:

On Apr 17, 12:49 pm, "Leigh Johnston" <le...@i42.co.uk> wrote:

A certain regular of this newsgroup thinks the following code is not w=

rong,

discuss.

void foo()
{
    std::vector<int> v;
    v.reserve(2);
    v.push_back(41);
    *(&v[0]+1) = 42;

}

The actual definition of "wrong" may vary from individual to individua=

l as

does common sense so it seems.

This may help:

If by wrong, you mean undefined behavior, then yes. The push_back is
fine, but the next line writes to an area which has been reserved but
not in the size. I know of several debug implementations of the
standard library which will crash horribly and report the error of the
code.

Example?

My mistake. I am incorrect. I thought visual studios debug iterators
would catch it. However, the undefined behavior line in question was
not using iterators but raw pointers. I was thinking of the following
example, which visual studios debug iterators do catch.

#include <vector>
using namespace std;
int main()
{
    std::vector<int> v;
    v.reserve(2);
    v.push_back(41);
    *(v.begin()+1) = 42;
}